1. Field of the Invention
The present invention relates to a compact rotary power cylinder. More particularly, the present invention relates to a compact rotary power cylinder comprising a pair of pistons reciprocally movable when a pressure impact is applied thereto and a torque stem rotatable to provide a torque in response to the reciprocal motion of the pair of pistons, wherein an improved connection is provided between the pistons and stem so as to render the power cylinder substantially compact as a whole while achieving a preferable torque characteristic.
2. Description of Relevant Art
The prior art to which the present invention is directed includes the art of compact rotary power cylinders being of a type in which a pair of pistons are fitted in a cylinder housing, separating such housing into a first chamber and a pair of second chambers, so as to be reciprocally movable when a pressure impact is supplied selectively to the first and second chambers, and a torque stem is provided through the cylinder housing perpendicularly to a reciprocal motion of the pistons so as to be rotatable in response to the reciprocal motion. Power cylinders of this type are generally used as accessory elements for actuation of final controls in process plants, typically to operate control valves which require a fast operation, such as when opening and closing a shut-off valve for filling beer or the like in a container. In such rotary power cylinders, therefore, it is essential that the overall size be minimized and the configuration be compact.
To meet such requirement there have been developed compact rotary power cylinders of the above-mentioned type in which an improvement is made such that the stem is operatively connected to the paired pistons with a pair of pivotable links provided therebetween.
With reference to FIG. 7 of the accompanying drawings, there is shown a horizontal sectional view of the aforesaid improved type of conventional compact rotary power cylinder.
Referring to FIG. 7, the conventional compact rotary power cylinder comprises a horizontal cylinder housing 40 having a pair of pistons 41, 42 slidably fitted therein and a vertical torque stem 43 rotatably provided therethrough. Housing 40 is thus separated by pistons 41, 42 into an intermediate chamber A and left and right chambers B, C. By selectively supplying a pressure impact into chambers A, B and C, pistons 41, 42 are reciprocally movable. In chamber A there is provided a link 44 pivotally connected on one side to stem 43 by a pin 44a and on the other side to piston 41 by another pin 44b. Likewise, there is provided another link 45 pivotally connected to stem 43 and piston 42 by pins 45a, 45b, respectively.
In the above arrangement, pivots 44a, 45a are disposed symmetrically with respect to the axis of stem 43 and, when the pressure impact is supplied to chamber A, travel from their original positions along respective arcuate paths to their final positions 44a', 45a', thereby rotating stem 43. Because of the overlapping provided between links 44, 45, the overall length of housing 40 is substantially reduced.
However, such arrangement has an attendant problem inasmuch as the original points of pivots 44a, 45 a are required to be angularly displaced toward the opposite direction relative to their final positions 44a', 45a' to achieve the overlapping between links 44, 45, thus resulting in a relatively small breakaway torque, which is disadvantageous in view of the fact that most final controls require relatively large breakaway torques.
Further, in the above arrangement, pistons 41, 42 are supported by pivotable links 44, 45 and are not sufficiently stable during their reciprocal motion including breakaway, thus adversely affecting the torque output characteristic of stem 43.